U.S. patent number 9,245,919 [Application Number 13/515,786] was granted by the patent office on 2016-01-26 for solid-state image pickup apparatus.
This patent grant is currently assigned to CANON KABUSHIKI KAISHA. The grantee listed for this patent is Junji Iwata, Masaya Ogino, Kentarou Suzuki, Yuichiro Yamashita. Invention is credited to Junji Iwata, Masaya Ogino, Kentarou Suzuki, Yuichiro Yamashita.
United States Patent |
9,245,919 |
Yamashita , et al. |
January 26, 2016 |
Solid-state image pickup apparatus
Abstract
Provided is a back-illuminated solid-state image pickup
apparatus having an improved color separation characteristic. A
photo detector includes a first photo detector unit and a second
photo detector unit disposed deeper than the first photo detector
unit with respect to a back surface of a semiconductor substrate,
wherein the first photo detector unit includes a
first-conductivity-type first semiconductor region where carriers
generated through photo-electric conversion are collected as signal
carriers. A readout portion includes a first-conductivity-type
second semiconductor region extending in a depth direction such
that the carriers collected in the first semiconductor region are
read out to a front surface of the semiconductor substrate. A unit
that reduces the amount of light incident on the second
semiconductor region is provided.
Inventors: |
Yamashita; Yuichiro (Ebina,
JP), Ogino; Masaya (Kawasaki, JP), Iwata;
Junji (Yokohama, JP), Suzuki; Kentarou (Kawasaki,
JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
Yamashita; Yuichiro
Ogino; Masaya
Iwata; Junji
Suzuki; Kentarou |
Ebina
Kawasaki
Yokohama
Kawasaki |
N/A
N/A
N/A
N/A |
JP
JP
JP
JP |
|
|
Assignee: |
CANON KABUSHIKI KAISHA (Tokyo,
JP)
|
Family
ID: |
43640626 |
Appl.
No.: |
13/515,786 |
Filed: |
December 13, 2010 |
PCT
Filed: |
December 13, 2010 |
PCT No.: |
PCT/JP2010/007224 |
371(c)(1),(2),(4) Date: |
June 13, 2012 |
PCT
Pub. No.: |
WO2011/074234 |
PCT
Pub. Date: |
June 23, 2011 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20120298841 A1 |
Nov 29, 2012 |
|
Foreign Application Priority Data
|
|
|
|
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Dec 18, 2009 [JP] |
|
|
2009-288461 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01L
27/14634 (20130101); H01L 27/14647 (20130101); H01L
27/14605 (20130101); H01L 27/14623 (20130101); H01L
27/1464 (20130101); H01L 27/14625 (20130101); H01L
27/14627 (20130101); H01L 27/14629 (20130101); H01L
27/14645 (20130101); H01L 27/1461 (20130101); H01L
27/14685 (20130101) |
Current International
Class: |
H01L
27/146 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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2005-268643 |
|
Sep 2005 |
|
JP |
|
2007-066962 |
|
Mar 2007 |
|
JP |
|
2007-080926 |
|
Mar 2007 |
|
JP |
|
2008-060476 |
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Mar 2008 |
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JP |
|
2008-270679 |
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Nov 2008 |
|
JP |
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2009-088415 |
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Apr 2009 |
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JP |
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2009-176777 |
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Aug 2009 |
|
JP |
|
2010-161254 |
|
Jul 2010 |
|
JP |
|
2008/026660 |
|
Mar 2008 |
|
WO |
|
Primary Examiner: Lee; John
Attorney, Agent or Firm: Canon USA, Inc. IP Division
Claims
The invention claimed is:
1. A back-illuminated solid-state image pickup apparatus
comprising: a semiconductor substrate including a plurality of
pixels, each pixel including a photo detector and a readout
portion; a wire disposed on a first main surface of the
semiconductor substrate; and a microlens disposed on a second main
surface of the semiconductor substrate opposite to the first main
surface and configured to focus light, wherein light enters the
photo detector from the second main surface of the semiconductor
substrate, wherein the photo detector includes a first photo
detector unit and a second photo detector unit disposed deeper than
the first photo detector unit with respect to the second main
surface, wherein the first photo detector unit includes a
first-conductive-type first semiconductor region in which carriers
generated through photo-electric conversion are collected as signal
carriers, wherein the readout portion includes a
first-conductive-type second semiconductor region extending in a
depth direction of the semiconductor substrate such that the
carriers collected at the first semiconductor region are read out
to the first main surface, and wherein the microlens is disposed
such that a projection of an edge of the microlens in the depth
direction intersects the second semiconductor region.
2. The solid-state image pickup apparatus according to claim 1,
wherein, the projection of the edge of the microlens in the depth
direction intersects at least two of the second semiconductor
regions corresponding to two of the first semiconductor regions
respectively included in two adjoining pixels of the plurality of
pixels.
3. The solid-state image pickup apparatus according to claim 1,
further comprising: a plurality of microlenses disposed on the
second main surface of the semiconductor substrate, each microlens
configured to focus light, wherein the microlenses are disposed in
a continuous manner such that the microlenses have an shared edge
which is a connection portion between the microlenses, and wherein
the microlenses are disposed such that a projection of the shared
edges of the microlenses intersects the second semiconductor
region.
4. The solid-state image pickup apparatus according to claim 1,
wherein, among the pixels, the first semiconductor region included
in a pixel is electrically conductive with the first semiconductor
region included in an adjoining pixel.
5. The solid-state image pickup apparatus according to claim 1,
further comprising: a microlens disposed on the second main surface
of the semiconductor substrate and configured to focus light,
wherein the center of the microlens substantially matches the
center of the first semiconductor region on a horizontal plane.
6. An image pickup system comprising: the solid-state image pickup
apparatus according to claim 1; and a signal processing unit
configured to process an image pickup signal output from the
solid-state image pickup apparatus.
7. The solid-state image pickup apparatus according to claim 1,
wherein the microlens is configured to reduce the amount of light
incident on the first-conductive-type second semiconductor region,
and wherein a light-level reduction ratio of the microlens for
light incident on the second semiconductor region is larger than
the light-level reduction ratio of the microlens for light incident
on the first semiconductor region.
8. A back-illuminated solid-state image pickup apparatus
comprising: a semiconductor substrate including a plurality of
pixels, each pixel including a photo detector and a readout
portion; a wire disposed on a first main surface of the
semiconductor substrate; and a plurality of microlens each disposed
on a second main surface of the semiconductor substrate opposite to
the first main surface and configured to focus light, wherein light
enters the photo detector from the second main surface of the
semiconductor substrate, wherein the photo detector includes a
first photo detector unit and a second photo detector unit disposed
deeper than the first photo detector unit with respect to the
second main surface, wherein the first photo detector unit includes
a first-conductive-type first semiconductor region in which
carriers generated through photo-electric conversion are collected
as signal carriers, wherein the readout portion includes a
first-conductive-type second semiconductor region extending in a
depth direction of the semiconductor substrate such that the
carriers collected at the first semiconductor region are read out
to the first main surface, wherein the plurality of microlens
include a first microlens and a second microlens disposed
continuously to each other, wherein the first microlens and the
second microlens have a connection portion therebetween having a
concave portion, and wherein a projection of a bottom of the
concave portion in the depth direction intersects the second
semiconductor region.
Description
TECHNICAL FIELD
The present invention relates to a back-illuminated solid-state
image pickup apparatus and a camera system.
BACKGROUND ART
A back-illuminated solid-state image pickup apparatus according to
the related art in which transistors and metal wires are arranged
on a first main surface (front surface) of a semiconductor
substrate and a second main surface (back surface) opposite to the
front surface is illuminated with light has been proposed to
provide a highly sensitive solid-state image pickup apparatus.
PTL 1 describes a back-illuminated solid-state image pickup
apparatus having photo detectors stacked in the depth direction of
a semiconductor substrate. The solid-state image pickup apparatus
described in PTL 1 detects, at the respective photo detectors,
light in wavelength bands corresponding to the respective depths of
the photo detectors, employing the fact that optical absorption
coefficient of the semiconductor substrate material is wavelength
dependent. For example, when three photo detectors are stacked, the
photo detector closest to the incident surface mainly detects blue
light, the photo detector in the middle mainly detects green light,
and the photo detector farthest from the incident surface mainly
detects red light.
In the solid-state image pickup apparatus described in PTL 1, the
photo detectors each have an impurity diffusion region extending in
the depth direction for electrically connecting the photo detectors
with circuits on the front surface.
With the configuration described in PTL 1, light enters the
impurity diffusion regions extending in the depth direction of the
semiconductor substrate. For example, when incident light is
photo-electrically converted at a position deep in an impurity
diffusion region corresponding to a blue photo detector, the
generated carriers are accumulated as signal charges for blue.
However, these carriers should actually be accumulated as signal
carriers for green and red. By accumulating the carriers as signal
carriers for blue, the color separation characteristic is
aggravated, causing noise.
A front incident solid-state image pickup apparatus includes
light-shielding structures, such as transistors and wires, on the
light incident surface. In contrast, with a back incident
solid-state image pickup apparatus, since transistors and wires are
not required on the incident surface, light is incident on the
entire back surface. Therefore, aggravation of the color separation
characteristic becomes more obvious.
The present invention has been conceived in light of the problem
described above and provides a back-illuminated solid-state image
pickup apparatus having an improved color separation
characteristic.
CITATION LIST
Patent Literature
PTL 1: Japanese Patent Laid-Open No. 2008-060476
SUMMARY OF INVENTION
A solid-state image pickup apparatus according to the present
invention includes a semiconductor substrate including a plurality
of pixels, each pixel including a photo detector and a readout
portion; a wire disposed on a first main surface of the
semiconductor substrate; and a light-level reducing portion,
wherein light enters the photo detector from a second main surface
of the semiconductor substrate opposite to the first main surface,
wherein the photo detector includes a first photo detector unit and
a second photo detector unit disposed deeper than the first photo
detector unit with respect to the second main surface, wherein the
first photo detector unit includes a first-conductive-type first
semiconductor region in which carriers generated through
photo-electric conversion are collected as signal carriers, wherein
the readout portion includes a first-conductive-type second
semiconductor region extending in a depth direction of the
semiconductor substrate such that the carriers collected at the
first semiconductor region are read out to the first main surface,
wherein the light-level reducing portion is configured to reduce
the amount of light incident on the first-conductive-type second
semiconductor region, and wherein a light-level reduction ratio of
the light-level reducing portion for light incident on the second
semiconductor region is larger than the light-level reduction ratio
of the light-level reduction portion for light incident on the
first semiconductor region.
With the solid-state image pickup apparatus according to the
present invention, it is possible to improve the color separation
characteristic.
Further features of the present invention will become apparent from
the following description of exemplary embodiments with reference
to the attached drawings.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is a schematic sectional view of a first embodiment.
FIG. 2 is a schematic top view of the first embodiment.
FIG. 3 is a potential distribution diagram in the horizontal
direction of the first embodiment.
FIG. 4 is a schematic top view of a second embodiment.
FIG. 5 is a schematic sectional view of a third embodiment.
FIG. 6 is a schematic sectional view of a fourth embodiment.
FIG. 7 is a schematic sectional view of a fifth embodiment.
FIG. 8A is a schematic sectional view of a sixth embodiment.
FIG. 8B is a potential distribution diagram in the horizontal
direction of the sixth embodiment.
FIG. 9A is a schematic top view of a seventh embodiment.
FIG. 9B is a schematic top view of photo detectors and microlenses
corresponding to blue light according to the seventh
embodiment.
FIG. 9C is a schematic top view of photo detectors and microlenses
corresponding to green light according to the seventh
embodiment.
FIG. 9D is a schematic top view of photo detectors and microlenses
corresponding to red light according to the seventh embodiment.
FIG. 10 is a potential distribution diagram in the horizontal
direction of the seventh embodiment.
FIG. 11 is a camera system according to an embodiment.
DESCRIPTION OF EMBODIMENTS
Embodiments of the present invention will be described with
reference to the drawings. In the embodiments, electrons are used
as signal carriers. Holes may also be used as signal carriers. When
using electrons as signal carriers, a first conductivity type is an
n-type, and a second conductivity type is a p-type. When holes are
used as signal carriers, the conductivity types of the
semiconductor regions are set opposite to those when electrons are
signal carriers.
First Embodiment
FIG. 1 is a schematic sectional view of a solid-state image pickup
apparatus according to a first embodiment of the present invention.
Semiconductor regions, such as photo detectors and transistors, are
included in the semiconductor substrate 101. A p-type semiconductor
or an SOI substrate may be used as the semiconductor substrate 101.
A circuit portion 102 is disposed on a first main surface (lower
side in the drawing) of the semiconductor substrate 101. The
circuit portion 102 includes transistors, electrodes, and wires. An
optical function portion is disposed on a second main surface
(upper side in the drawing), i.e., a side opposite to that on which
the circuit portion 102 is disposed, with an insulating layer and a
protective layer interposed between the optical function portion
and the second main surface. In the back-illuminated solid-state
image pickup apparatus according to this embodiment, light enters
from the surface opposite to the first main surface (front surface)
on which wires and transistors are disposed, i.e., from the second
main surface (back surface).
In this embodiment, the optical function portion includes a
microlens. As described in detail below, the microlens functions as
a light-level reducing portion.
Next, the structure of a photo detector disposed on the
semiconductor substrate 101 will be described. As illustrated in
FIG. 1, n-type semiconductor regions 103B, 103G, and 103R are
stacked in the depth direction in the semiconductor substrate 101.
In this specification, the depth direction is a direction
perpendicular to the front surface or back surface of the
substrate. The horizontal direction is a direction orthogonal to
the depth direction.
The n-type semiconductor regions 103B, 103G, and 103R each form a
p-n junction with a p-type semiconductor region 104. In the n-type
semiconductor region 103B closest to the back surface, electrons
that are generated through photo-electric conversion of light in
the blue wavelength band are mainly collected. In the n-type
semiconductor region 103G disposed deeper than the n-type
semiconductor region 103B with respect to the back surface,
electrons generated through photo-electric conversion of light in
the green wavelength band are mainly collected. In the n-type
semiconductor region 103R disposed deepest with respect to the back
surface, electrons generated through photo-electric conversion of
light in the red wavelength band are mainly collected. In this
embodiment, the n-type semiconductor region 103B is equivalent to a
first semiconductor region according to the present invention, and
the n-type semiconductor region 103G is equivalent to a third
semiconductor region according to the present invention.
In this way, each of the n-type semiconductor regions 103B, 103G,
and 103R together with the p-type semiconductor region 104
constitute a photo detector, or, specifically, a photodiode. In
each photo detector, light in a wavelength region corresponding to
the depth of the photo detector is detected.
N-type semiconductor regions 105B and 105G are readout portions
that extract the carriers collected in the n-type semiconductor
regions 103B and 103G, respectively. The n-type semiconductor
region 105B extends in the depth direction of the semiconductor
substrate 101 from the n-type semiconductor region 103B to the
front surface. The n-type semiconductor region 105G extends in the
depth direction of the semiconductor substrate 101 from the n-type
semiconductor region 103G to the front surface. It is desirable
that the impurity concentrations of the n-type semiconductor
regions 105B and 105G be respectively higher than those of the
n-type semiconductor regions 103B and 103G. In this embodiment, the
n-type semiconductor region 105B is equivalent to a second
semiconductor region according to the present invention, and the
n-type semiconductor region 105G is equivalent to a fourth
semiconductor region according to the present invention.
In this embodiment, since the n-type semiconductor region 103R
corresponding to the red wavelength band is disposed at the front
surface, the readout portion corresponding to the n-type
semiconductor region 103R can be omitted. The n-type semiconductor
region 103R may also be embedded into the semiconductor substrate
101 such that it is not exposed at the front surface. In such a
case, a readout portion corresponding to the n-type semiconductor
region 103R should be provided.
Each readout portion is not limited to such shape and position so
long as it has a function for extracting signals based on electrons
generated at the photo detectors to the front surface via a readout
portion.
In this embodiment, the three n-type semiconductor regions 103B,
103G, and 103R, which are stacked in the depth direction, and the
n-type semiconductor regions 105B and 105G are all included in a
single pixel. Although only two pixels are illustrated in FIG. 1,
actually, multiple pixels are arranged in a line or in a matrix.
This is also the true for the other embodiments described
below.
The circuit portion 102 includes a circuit that reads out signals
based on electrons generated at the photo detectors. An example
configuration of the circuit portion 102 will be described in
detail.
The n-type semiconductor regions 105B and 105G and the n-type
semiconductor region 103R are electrically connected with the input
of an amplifier via transfer MOS transistors TxB, TxG, and TxR. The
input of the amplifier can be connected to a power source via a
reset MOS transistor Res. By turning on the transfer MOS
transistors, fully depleted transfer of the electrons generated at
the photo detectors can be performed to the input of the amplifier
via the readout portions.
The amplifier is an amplifier MOS transistor M. The gate of the
amplifying MOS transistor M is the input. One of the source and
drain is connected to the power source, and the other is connected
to the source or the drain of a selector MOS transistor SEL. One of
the source and drain of the selector MOS transistor SEL that is not
connected to the amplifier MOS transistor M is connected to an
output line. The configuration is not limited thereto, and the
semiconductor regions may be electrically connected directly with
the output lines.
Microlenses 106 that collect light are disposed on the back surface
of the semiconductor substrate 101. The microlenses 106 are
disposed at positions corresponding to the positions of the photo
detectors. In this embodiment, one microlens 106 is disposed for
each group of three stacked photo detectors. In other words, the
projection of the microlens 106 in the depth direction covers the
photo detectors. In this embodiment, an edge of the microlens 106
is positioned above the n-type semiconductor region 105B. In other
words, the projection of the microlens 106 in the depth direction
overlaps the n-type semiconductor region 105B. The microlens 106
may be disposed a certain distance away from the back surface or
may be disposed directly on the back surface.
Incident light converges at the center of the microlens 106.
Therefore, the amount of light incident on the n-type semiconductor
region 105B disposed below the edge of the microlens 106 is reduced
from that when the microlens 106 is not provided. The reduction
ratio of the amount of incident light is the ratio of the reduction
amount by providing the microlens 106 to the amount of the incident
light when the microlens 106 is not provided.
The amount of light incident on the n-type semiconductor region
103B is substantially unchanged or is increased by converging at
the microlens 106. In other words, the reduction ratio is
substantially zero, or the amount of incident light does not
decrease but, instead, increases.
In this way, with the light-level reducing portion according to the
present invention, the reduction ratio of the amount of incident
light on the second semiconductor region is larger than the
reduction ratio of the amount of incident light on the first
semiconductor region. The amount of light incident on the first
semiconductor region is not reduced at all or, instead, may be
increased. The light-level reducing portion may completely block
the light incident on the second semiconductor region such that the
amount of light incident on the second semiconductor region is
zero.
FIG. 2 is a top view of this embodiment. FIG. 2 illustrates the
n-type semiconductor regions 103B, 1036, and 103R and the n-type
semiconductor regions 105B and 105G.
As illustrated in the drawing, the projections of the three n-type
semiconductor regions 103B, 103G, and 103R in the depth direction
overlap. The n-type semiconductor regions 105B and 105G, which are
readout portions, are disposed to correspond to the n-type
semiconductor regions 103B, 103G, respectively. When viewed from
the top, the n-type semiconductor regions 103B, 1036, and 103R are
overlaid with the microlens 106.
When viewed from the top, the edge of the microlens 106 intersects
the n-type semiconductor region 105B. In other words, the
projection of the microlens 106 in the depth direction overlaps the
n-type semiconductor region 105B.
In this embodiment, the n-type semiconductor region 103B disposed
closest to the back surface has the largest area on a horizontal
plane. The microlens 106 is disposed such that its center
substantially matches the center of the n-type semiconductor region
103B.
FIG. 3 is a potential distribution diagram of this embodiment in
the horizontal direction. FIG. 3 illustrates the potential
distribution in the horizontal direction at depths corresponding to
the positions of the n-type semiconductor regions 103B, 103G, and
103R. In other words, FIG. 3 illustrates the potential
distributions along lines A, B, and C in FIG. 1. The vertical axis
represents the potential of electrons, and the horizontal axis
represents the horizontal position.
As illustrated in FIG. 3, a potential barrier formed by the p-type
semiconductor region 104 is interposed between the n-type
semiconductor regions 103B of adjoining pixels. The potential of
the n-type semiconductor region 105B, which is a readout portion,
is lower than the potential of the n-type semiconductor region
103B. At this depth, light mainly in the blue wavelength region is
photo-electrically converted and is collected in the n-type
semiconductor region 103B as blue signal carriers.
When there is a flat section in the potential barrier between the
pixels, carriers generated in this flat section diffuses to the
depth direction and may enter the n-type semiconductor region 103G.
Therefore, it is desirable that the n-type semiconductor region
103B widely extend in the horizontal direction. By reducing the
distance between n-type semiconductor regions 103B in adjoining
pixels, the flat section in the potential barrier becomes small,
and, thus, the electrons reach the n-type semiconductor region 103B
more easily than reaching the n-type semiconductor region 103G.
That is, color mixing within a pixel can be prevented.
Another method of preventing color mixing will be described. The
microlens 106 is disposed such that its center matches the center
of the n-type semiconductor region 103B, and light is allowed to
enter the n-type semiconductor region 103B. In this way, the amount
of light entering the potential barrier interposed between
adjoining pixels decreases, and, as a result, the amount of
electrons that may enter the above-described n-type semiconductor
region 103G is reduced.
FIG. 3 illustrates a potential distribution in the horizontal
direction at the depth corresponding to the position of the n-type
semiconductor region 103G. The n-type semiconductor region 105G,
which is the readout portion, has a potential lower than that of
the n-type semiconductor region 103G.
A potential barrier is formed between the n-type semiconductor
region 105G and the n-type semiconductor region 105B. It is
desirable that the n-type semiconductor region 105G and the n-type
semiconductor region 105B be electrically separated in this
way.
At this depth, light mainly in the green wavelength band is
photo-electrically converted and collected in the n-type
semiconductor region 103G as green signal carriers. On the other
hand, when light is incident on the n-type semiconductor region
105B, the carriers generated by photo-electric conversion is
collected as blue signal carriers.
In this embodiment, since the horizontal positional relationship is
such that the edge of the microlens 106 is disposed above the
n-type semiconductor region 105B, the amount of light incident on
the n-type semiconductor region 105B decreases. Therefore, carriers
to be collected as green signal carriers less likely enter the
n-type semiconductor region 105B.
FIG. 3 illustrates a potential distribution in the horizontal
direction at a depth corresponding to the position of the n-type
semiconductor region 103R. As illustrated in FIG. 3, potential
barriers are formed between the n-type semiconductor region 105B
and the n-type semiconductor region 105G, and between the n-type
semiconductor region 105G and the n-type semiconductor region 103R.
It is desirable that the n-type semiconductor region 105B, the
n-type semiconductor region 105G, and the n-type semiconductor
region 103R be electrically separated in this way.
At this depth, light mainly in the red wavelength band is
photo-electrically converted and collected in the n-type
semiconductor region 103R as red signal carriers. By disposing the
microlens 106, red signal carriers less likely enter the n-type
semiconductor region 105B.
As described above, in this embodiment, the projection of the edge
of the microlens 106 in the depth direction overlaps the n-type
semiconductor region 105B. In other words, when viewed from the
top, the n-type semiconductor region 105B is overlaid with the
microlens 106. Since the amount of light incident on the n-type
semiconductor region 105B decreases in such a configuration,
carriers are less likely generated at a deep position relative to
the back surface of the n-type semiconductor region 105B.
Consequently, the color separation characteristic is improved.
In this embodiment, the center of the n-type semiconductor region
103B substantially matches the center of the microlens 106 on the
horizontal plane. With such a configuration, carriers are less
likely generated in the region between the n-type semiconductor
regions 103B in adjoining pixels. Consequently, the color
separation characteristic is improved.
Second Embodiment
A solid-state image pickup apparatus according to another
embodiment of the present invention is illustrated in FIG. 4. FIG.
4 is a top view of the solid-state image pickup apparatus.
Components that have the same functions as those in the first
embodiment will be represented by the same reference numerals, and
detailed descriptions thereof will not be repeated.
In this embodiment, when viewed from the top, the edge of the
microlens 106 intersects the n-type semiconductor region 105B and
the n-type semiconductor region 105G. The microlenses 106 in
adjoining pixels are disposed in a connected manner such that they
share part of their edge. In this way, when part or all of a
microlens 106 is connected with the microlens 106 of the adjoining
pixel, a section that appears as a valley in a sectional view also
correspond to the edge of the microlens 106. It is desirable that
the edge shared by adjoining microlenses 106 be positioned above
the n-type semiconductor regions 105B and 105G.
Similar to the n-type semiconductor region 105B according to the
first embodiment, in this embodiment, the amount of light incident
on the n-type semiconductor region 105G decreases. Therefore, the
amount of carriers generated in the n-type semiconductor region
1056 at a depth corresponding to the position of the n-type
semiconductor region 103R decreases. That is, carriers to be
collected as red signal carriers are less likely collected as green
carriers.
In addition to the above-described advantages of the first
embodiment, this embodiment has the following advantage.
In this embodiment, when viewed from the top, the edge of the
microlens 106 intersects the n-type semiconductor region 105B and
the n-type semiconductor region 105G. Since the amount of light
incident on the n-type semiconductor region 105G can be reduced
with such a configuration, carriers are less likely generated at a
position deep with respect to the back surface of the n-type
semiconductor region 105G. Consequently, the color separation
characteristic is improved.
Third Embodiment
FIG. 5 is a schematic sectional view of a solid-state image pickup
apparatus according to another embodiment of the present invention.
Components that have the same functions as those in the first or
second embodiment will be represented by the same reference
numerals, and detailed descriptions thereof will not be
repeated.
The configuration according to this embodiment includes
light-shielding portions 107 on the back surface, which is the
light incident surface. As described below, in this embodiment, the
light-shielding portions 107 function as light-level reducing
portions.
The light-shielding portions 107 are made of a material that does
not transmit light. For example, a metal such as aluminum is used.
Instead, a light-absorbing material, such as black-colored resin,
may be used. Each light-shielding portion 107 is disposed above the
n-type semiconductor region 105B. The horizontal positional
relationship is determined such that the projection of the
light-shielding portion 107 in the depth direction overlaps the
n-type semiconductor region 105B. The light-shielding portion 107
may be positioned such that at least part of the incident light is
blocked.
The light-shielding portion 107 blocks part of the incident light,
and thus, the amount of light incident on the n-type semiconductor
region 105B decreases. Photo-electric conversion of light in the
green wavelength band and red wavelength band is less likely
performed in deep sections of the n-type semiconductor region 105B.
As a result, the carriers that should be read out as green or red
signal carriers are less likely read out as blue signal
carriers.
The light-shielding portion 107 may be interposed between the
n-type semiconductor regions 103B of adjoining pixels. In this way,
the amount of light incident on the region between the n-type
semiconductor regions 103B of adjoining pixels can be reduced, and
thus, the amount of carriers generated at a depth corresponding to
the position of the n-type semiconductor region 103B and entering
the n-type semiconductor region 103G decreases.
As described above, in this embodiment, the projection of the
light-shielding portion 107 in the depth direction overlaps the
n-type semiconductor region 105B. In other words, when viewed from
the top, the n-type semiconductor region 105B is overlaid with the
light-shielding portion 107. Since the amount of light incident on
the n-type semiconductor region 105B can be reduced with such a
configuration, the generation of carriers at a deep position with
respect to the back surface of the n-type semiconductor region 105B
can be suppressed. Consequently, the color separation
characteristic is improved.
By interposing the light-shielding portion 107 between the n-type
semiconductor regions 103B of adjoining pixels, the generation of
carriers between the n-type semiconductor regions 103B of adjoining
pixels can be suppressed. Consequently, the color separation
characteristic is improved even more.
In addition to the configuration according to this embodiment, by
combining the microlenses according to the first or second
embodiment, the color separation characteristic can be improved
even more.
Fourth Embodiment
FIG. 6 is a schematic sectional view of a solid-state image pickup
apparatus according to another embodiment of the present invention.
Components that have the same functions as those in the first to
third embodiments will be represented by the same reference
numerals, and detailed descriptions thereof will not be
repeated.
In this embodiment, an optical waveguide 108 is disposed on the
back surface, which is the light incident surface. As described
below, the optical waveguide 108 according to this embodiment
function as a light-level reducing portion.
The optical waveguide 108 includes a core portion 109 and clad
portions 110. It is desirable that the core portion 109 be made of
a material that transmits light and has a small index of
refraction. The clad portions 110 are made of a material that has
an index of refraction larger than that of the core portion 109.
Instead, a material that reflects light may be used.
In this embodiment, each clad portion 110 is positioned above the
n-type semiconductor region 105B. The projection of the clad
portion 110 in the depth direction overlaps the n-type
semiconductor region 105B.
Since incident light is reflected at the clad portion 110, the
amount of light incident on the n-type semiconductor region 105B
decreases. Therefore, photo-electric conversion of light in the
green wavelength band and red wavelength band is less likely
performed in deep sections of the n-type semiconductor region 105B.
As a result, the carriers that should be read out as green or red
signal carriers are less likely read out as blue signal
carriers.
In this embodiment, by forming the optical waveguide 108 long in
the depth direction, the directionality of the incident light is
improved. Light that enters the optical waveguide 108 at a certain
incident angle is reflected at and interferes with the clad
portions 110. When the light reaches the second main surface of the
semiconductor substrate, the influence of the incident angle is
weakened, and the light becomes substantially parallel.
When a large amount of the incident light is oblique, the
solid-state image pickup apparatus including stacked photo
detectors will have an unsatisfactory color separation
characteristic. Therefore, by using an optical waveguide that is
long in the depth direction, the color separation characteristic
can be improved.
As described above, in this embodiment, the projection of the clad
portion 110 in the depth direction overlaps the n-type
semiconductor region 105B. That is, when viewed from the top, the
n-type semiconductor region 105B is overlaid with the clad portion
110. Since the amount of light incident on the n-type semiconductor
region 105B can be reduced with such a configuration, the
generation of carriers at a deep position with respect to the back
surface of the n-type semiconductor region 105B can be suppressed.
Consequently, the color separation characteristic is improved.
In addition to the configuration according to this embodiment, by
combining the microlenses according to the first or second
embodiment, the color separation characteristic can be improved
even more.
Fifth Embodiment
FIG. 7 is a schematic sectional view of a solid-state image pickup
apparatus according to another embodiment of the present invention.
Components that have the same functions as those in the first to
fourth embodiments will be represented by the same reference
numerals, and detailed descriptions thereof will not be
repeated.
In this embodiment, a pillar-type microlens 111 is disposed on the
back surface for each pixel. As described below, in this
embodiment, the pillar-type microlenses 111 function as light-level
reducing portions.
An air gap 112 is formed between the microlenses 111 of adjoining
pixels. The projection of the air gap 112 in the depth direction
overlaps the n-type semiconductor region 105B. That is, when viewed
from the top, the n-type semiconductor region 105B is overlaid with
the air gap 112.
The air gap 112 is a vacuum or is filled with nitrogen or air. The
difference in the indices of refraction of the air gap 112 and the
pillar-type microlens 111 causes the light incident on the air gap
112 to converge into the microlens 111.
Since the air gap 112 is disposed above the n-type semiconductor
region 105B, the amount of light incident on the n-type
semiconductor region 105B can be reduced. Therefore, photo-electric
conversion of light in the green wavelength band and red wavelength
band is less likely performed in deep sections of the n-type
semiconductor region 105B. As a result, the carriers that should be
read out as green or red signal carriers are less likely read out
as blue signal carriers.
Since the microlens 111 is pillar-type, the directionality of the
incident light is improved. Light that enters the microlens 111 at
a certain incident angle is reflected at and interferes with the
air gap 112. When the light reaches the second main surface of the
semiconductor substrate, the influence of the incident angle is
weakened, and the light becomes substantially parallel.
When a large amount of the incident light is oblique, the
solid-state image pickup apparatus including stacked photo
detectors will have an unsatisfactory color separation
characteristic. Therefore, by using microlenses having excellent
directionality of light, the color separation characteristic can be
improved.
As described above, in this embodiment, the projection of the air
gap 112 formed between the pillar-type microlenses in the depth
direction overlaps the n-type semiconductor region 105B. That is,
when viewed from the top, the n-type semiconductor region 105B is
overlaid with the air gap 112.
Since the amount of light incident on the n-type semiconductor
region 105B can be reduced with such a configuration, the
generation of carriers in a deep position with respect to the back
surface of the n-type semiconductor region 105B can be suppressed.
Consequently, the color separation characteristic is improved.
In addition to the configuration according to this embodiment, by
combining the light-level reducing portions of the third embodiment
and/or the optical waveguide of the fourth embodiment, the color
separation characteristic is improved even more.
Sixth Embodiment
FIG. 8A is a schematic sectional view of a solid-state image pickup
apparatus according to another embodiment of the present invention.
Components that have the same functions as those in the first to
fifth embodiments will be represented by the same reference
numerals, and detailed descriptions thereof will not be
repeated.
In this embodiment, the n-type semiconductor regions 103B of
adjoining pixels are electrically conductive. The n-type
semiconductor regions 103B may be electrically conductive when a
p-type semiconductor region is not provided between the n-type
semiconductor regions 103B. Even when a p-type semiconductor region
is provided, the n-type semiconductor regions 103B may be
electrically conductive when the n-type semiconductor regions 103B
are sufficiently close to each other and connected with a depletion
layer.
In FIG. 8A, a depletion layer 113 extending from the n-type
semiconductor regions 103B is indicated by dotted lines. As
illustrated in FIG. 8A, the n-type semiconductor regions 103B of
adjoining pixels are electrically conductive via the depletion
layer 113.
FIG. 8B illustrates a potential distribution in the horizontal
direction at a depth corresponding to the position of the n-type
semiconductor regions 103B. That is, FIG. 8B illustrates the
potential distribution along line D in FIG. 8A. In FIG. 8B, the
vertical axis represents the potential of electrons, and the
horizontal axis represents the horizontal position.
As illustrated in FIG. 8B, a potential barrier formed between the
n-type semiconductor regions 103B of two different pixels does not
have a flat section. In other words, the potential barrier formed
between the n-type semiconductor regions 103B of two different
pixels has a potential gradient that causes carriers to drift
toward one of the pixels in the horizontal direction.
When there is a flat section in the potential barrier, as described
in the first embodiment, carriers enter the n-type semiconductor
regions 103G. In this embodiment, since the potential barrier has
substantially no flat sections, carriers less likely enter the
n-type semiconductor regions 103G.
When an impurity diffusion region extends across adjoining pixels,
a potential barrier is formed in the depth direction also in the
region between the n-type semiconductor regions 103B of the
adjoining pixels. Consequently, carriers less likely enter the
n-type semiconductor regions 103G.
FIG. 8A illustrates microlenses 106, which are similar to those of
the first embodiment, disposed on the back surface. In this
embodiment, the configuration is not limited thereto, and
configurations of other embodiments may be employed.
As described above, in addition to the advantages of the first to
fifth embodiments, this embodiment has the following advantage.
In this embodiment, the n-type semiconductor regions 103B of
adjoining pixels are electrically conductive. With such a
configuration, carriers that are generated between the n-type
semiconductor regions 103B of adjoining pixels less likely enter
the n-type semiconductor regions 103G. Consequently, the color
separation characteristic is improved even more.
In this embodiment, the n-type semiconductor regions 103B are
electrically conductive. Instead, however, the n-type semiconductor
regions 103G of adjoining pixels may be electrically conductive in
a similar manner. In such a case, carriers that are generated in
the region between the n-type semiconductor regions 103G of
adjoining pixels less likely enter the n-type semiconductor regions
103B and the n-type semiconductor regions 103R.
Seventh Embodiment
FIG. 9A is a top view of a solid-state image pickup apparatus
according to another embodiment of the present invention.
Components that have the same functions as those in the first to
sixth embodiments will be represented by the same reference
numerals, and detailed descriptions thereof will not be
repeated.
In this embodiment, when viewed from the top, the edge of the
microlens 106 intersects the center of the n-type semiconductor
region 103B. In addition, when viewed from the top, the edge of the
microlens 106 intersects the center of the n-type semiconductor
region 103G. In other words, one microlens 106 is disposed above
two n-type semiconductor regions 103B. That is, the projection of
the microlens 106 in the depth direction overlaps two of the n-type
semiconductor regions 103B. This is also the same for the n-type
semiconductor regions 103G.
The n-type semiconductor regions 105B and 105G, which are readout
portions, are disposed at the centers of the n-type semiconductor
regions 103B and 103G, respectively. In other words, the projection
of the edge of the microlens 106 in the depth direction intersects
the n-type semiconductor regions 105B and 105G.
FIG. 9B is a top view of the microlenses 106, the n-type
semiconductor regions 103B, and the n-type semiconductor regions
105B. As illustrated in FIG. 9B, each microlens 106 overlaps two
n-type semiconductor region 103B adjoining each other in the
left-to-right direction in the drawing. When viewed from the top,
the edge of one microlens 106 intersects two n-type semiconductor
regions 105B.
FIG. 9C is a top view of the microlenses 106, the n-type
semiconductor regions 103G, and the n-type semiconductor regions
105G. The n-type semiconductor regions 103G surround the areas
where the n-type semiconductor regions 105B are provided. Each
microlens 106 overlaps two n-type semiconductor regions 103G
adjoining each other in the top-to-bottom direction in the drawing.
When viewed from the top, the edge of one microlens 106 intersects
two n-type semiconductor regions 105G.
FIG. 9D is a top view of the microlenses 106 and the n-type
semiconductor regions 103R. As illustrated in FIG. 9D, the centers
of the microlenses 106 match the centers of the n-type
semiconductor regions 103R.
As illustrated in FIG. 9A, the n-type semiconductor regions 105B
and 105G are disposed at the centers of the n-type semiconductor
regions 103B 103G, respectively. When viewed from the top, the
n-type semiconductor regions 105B and the n-type semiconductor
regions 103G are positioned such that they form a tetragonal
face-centered lattice. That is, four n-type semiconductor regions
105B are positioned at the apices of a regular tetragon with one
n-type semiconductor region 105G positioned at the center. Each of
the four n-type semiconductor regions 105B are also positioned at
the center of a regular tetragon with four n-type semiconductor
regions 105G at the apices. The peripheral pixels are not limited
such positional relationship.
With such a configuration, the distance between adjoining readout
portions can be increased. It is desirable that the impurity
concentration of the n-type semiconductor regions 105B and 105G,
which are readout portions, be high. When impurity concentration is
high, impurities diffuse more easily. Furthermore, a high impurity
concentration increases the spreading of the depletion layer in the
p-type semiconductor region 104 in the vicinity. Accordingly, when
the distance between the n-type semiconductor region 105B and the
n-type semiconductor region 105G is small, these regions may become
electrically conductive. Thus, it is desirable that the distance
between adjoining readout portions be large.
FIG. 10 illustrates the potential distribution in the horizontal
direction along line E in FIG. 9B and at a depth corresponding to
the position of the n-type semiconductor regions 103B. The vertical
axis represents the potential of electrons, and the horizontal axis
represents the horizontal position.
In this embodiment, two of the n-type semiconductor regions 103B
are disposed below one microlens 106. Therefore, a potential
barrier formed between adjoining n-type semiconductor regions 103B
is positioned below the microlens 106. In FIG. 10, the potential
barrier is positioned at the center of the microlens 106. When
light focused by the microlens 106 is photo-electrically converted,
the generated carriers are collected to one of the adjoining n-type
semiconductor regions 103B on the left and right sides in FIG.
10.
In this embodiment, one microlens 106 corresponds to one pixel.
Thus, to acquire a blue signal from one pixel, the average value of
signals from adjoining n-type semiconductor regions 103B on the
left and right sides in FIG. 9B may be determined. Similarly, to
acquire a green signal from one pixel, the average value of signals
from adjoining n-type semiconductor regions 103G on the upper and
lower sides in FIG. 9C may be determined.
In this embodiment, a pixel includes two n-type semiconductor
regions 103B while sharing them with the pixels on the left and
right. Similarly, a pixel includes two n-type semiconductor regions
103G while sharing them with the pixels above and below.
The edge of the microlens 106 intersects the n-type semiconductor
regions 105B and 105G, which are readout portions. With such a
configuration, each pixel shares readout portions with adjoining
pixels.
FIGS. 9A, 9B, 9C, 9D, and 10 illustrate a configuration in which
microlenses 106, which are similar to those in the first
embodiment, are disposed on the back surface. This embodiment is
not limited thereto and may employ other embodiments.
As described above, in addition to the advantages of the first to
sixth embodiments, this embodiment has the following advantage.
With this embodiment, the distance between the n-type semiconductor
regions 105B and 105G can be set large. With such a configuration,
the electric conductivity between the n-type semiconductor regions
105B and 105G can be reduced, and thus, the color separation
characteristic is improved even more.
Eighth Embodiment
A camera system including a solid-state image pickup apparatus
according to an embodiment of present invention will be described
in detail. Examples of an image pickup system include digital still
cameras and digital camcorders. FIG. 11 is a block diagram
illustrating an example image pickup system in which a
photoelectric conversion apparatus is applied to a digital still
camera.
FIG. 11 illustrates a barrier 1 that protects a lens 2, which forms
an optical image of a subject on a solid-state image pickup
apparatus 4, and an aperture stop 3 that varies the amount of light
transmitted through the lens 2. The solid-state image pickup
apparatus 4 is solid-state image pickup apparatuses of one of the
embodiments described above and converts an optical image formed by
the 2 to image data. The substrate of the solid-state image pickup
apparatus 4 is provided with an A/D converter. A signal processing
unit 7 performs various corrections on image pickup data output
from the solid-state image pickup apparatus 4 and compresses data.
FIG. 11 also illustrates a timing generator 8 that outputs various
timing signals to the solid-state image pickup apparatus 4 and the
signal processing unit 7, and a total control/computation unit 9
that performs various computations and controls the entire digital
still camera. Image data is temporarily stored in a memory 10. An
interface unit 11 is used to record to and read out from a
recording medium. A detachable recording medium, such as a
semiconductor memory, is used to record and read out image pickup
data. An interface unit 13 is used to communicate with an external
computer, etc. The timing signals may be input from a unit outside
the image pickup system, so long as the image pickup system
includes at least the solid-state image pickup apparatus 4 and the
signal processing unit 7 that processes the image pickup signal
output from the solid-state image pickup apparatus 4.
In this embodiment, the solid-state image pickup apparatus 4 and
the A/D converter are provided on the same substrate. Instead,
however, the solid-state image pickup apparatus 4 and the A/D
converter may be provided on separate substrates. Furthermore, the
solid-state image pickup apparatus 4 and the signal processing unit
7 may be provided on the same substrate.
As described above, the solid-state image pickup apparatus
according to an embodiment of the present invention can be applied
to a camera system. By applying the solid-state image pickup
apparatus according to the present invention to a camera system, an
image having improved color separation characteristic can be
captured.
In each embodiment, a solid-state image pickup apparatus having
three photo detectors is described. However, the present invention
can be applied so long as a plurality of stacked photo detectors is
included. For example, the present invention can be applied to a
back-illuminated solid-state image pickup apparatus having two
stacked photo detectors.
While the present invention has been described with reference to
exemplary embodiments, it is to be understood that the invention is
not limited to the disclosed exemplary embodiments. The scope of
the following claims is to be accorded the broadest interpretation
so as to encompass all such modifications and equivalent structures
and functions.
This application claims the benefit of Japanese Patent Application
No. 2009-288461, filed Dec. 18, 2009, which is hereby incorporated
by reference herein in its entirety.
REFERENCE SIGNS LIST
101 semiconductor substrate
102 circuit portion
103 n-type semiconductor region
104 p-type semiconductor region
105 n-type semiconductor region
106 microlens
107 light-shielding portion
108 optical waveguide
109 core portion
110 clad portion
111 pillar-type microlens
112 air gap
113 depletion layer
* * * * *